mappedTypes.ts

type Events = {
  add: string;
  remove: string;
  move: string;
};

type EventKeys = keyof Events;

const userActions: OnEvent = {
  onAdd: () => {},
  onRemove: () => {},
  onMove: () => {},
};

type OnEvent = {
  [Key in EventKeys as `on${Capitalize<Key>}`]: () => any
};